Mat Colegate gives some serious Thor-t to the latest in the Avengers series. Is it a stark day for the franchise or a real (widow's) peak?

An actor friend of mine once told me that one of the most difficult facial expressions for any Thespian to pull off was 'tired but elated'. Try it in a mirror and you'll see his point. When we non-Rada types try it it looks a bit more like 'confused by invisible spinach in my teeth'. However it is a look that Joss Whedon, director of Avengers: Age Of Ultron has perfected, if his delightedly knackered appearance before last night's screening is anything to go by. He hoped we'd enjoy it - he even went as far as to beg us to enjoy it - all the while sporting the kind of expression more commonly seen on the faces of men who've just run up mountains with sacks full of rocks tied to their backs.

And its hard to begrudge him his pains, because Age Of Ultron is massive. Hugely ambitious, straddling locations like a spandex clad colossus of Rhodes and boasting the most far-reaching and apocalyptic story in the entire Marvel film franchise so far. It's an enormously impressive undertaking. But what's even more impressive is how successful it is. It isn't perfect, but, like the classic comic book stories it draws upon, it's bold, colourful, inspiring and chock full of heart.

Age Of Ultron is basically a science-gone-bad story. Tony Stark (AKA Iron Man, played to pithy perfection once more by Robert Downey Jr.), creates an artificial intelligence system to protect the world from alien invasion - “peace in our time”, as the genius playboy puts it. Said intelligence system has other ideas and decides that the main threat to said peace is (DER DER DURRRRRRRR) humanity itself. Mayhem ensues, cities are levelled and lots (and lots and lots and lots) of robots get hammered, zapped, shielded, hulked and generally pounded into pencil sharpeners. It's not complicated stuff when you put it like that.

However its an extremely complicated job to realise it all and make it run smooth, and thankfully Whedon is up to it. The main reason the director was such an inspired choice to helm the flagship films of the Marvel series is his knack for getting audiences up to speed quickly and with an absolute minimum of boringly info-heavy dialogue. It's something he first showed a talent for with Serentity, in which his ill-fated TV show Firefly was rounded out and it's considerable cast introduced to new viewers without once leaving them behind. This ability to appeal to the fan community as well as the weekend popcorn munchers made him the obvious choice when it came to steering cinema audiences through Marvel comic's slippery, knotty and exhausting continuity. Whedon has a knack for getting to the heart of each character within a few well chosen (and often very funny) lines, and he can illuminate concepts that a lot of directors would spend entire films hammering into the ground in a single scene.

A case in point: During Age Of Ultron The Avengers have to travel to Wakanda, an imaginary African region that looms large in Marvel's comic book continuity. There they encounter Andy Serkis' delightfully hideous arms dealer Ulysses Klaw, uncover more of Ultron's plan and give Tony Stark a chance to reflect upon and rue his previous job making a living in the arms trade. There's also a massive fight. Whedon does all of this in ten minutes: Introducing a fresh new corner of the Marvel universe, a new recurring villain, illuminating a previously obscured aspect of one of his massive main cast and also causing merry havoc as Hulk and Iron Man square up for one of the most exciting rumbles in the entire series. That's quick and efficient work. That he makes you actually care about it all is even more impressive.

The familiar faces are all here of course. Once again special mention has to be given to Chris Hemsworth as Thor, who plays the Asgardian prince with just the right amount of pomposity and self-deprecation, and Chris Evans' Captain America, who... look Chris Evans just is Captain America, OK? Scarlett Johansson and Mark Ruffalo both get moments to shine as Black Widow and Bruce Banner (AKA The Hulk, who's on even more chortle inducingly destructive form this time round), but the stand out performance this time is from Jeremy Renner, whose Hawkeye – 'just a guy with a bow and arrow' – has the task of being the heart and soul of the whole team in a way that shows up his flaws while also convincing you that he's the fulcrum around which their entire dynamic swings.

The action sequences, despite their enormous size, are extremely efficient. There's none of the confusion and bad movement plotting that made the conclusion of Captain America: The Winter Soldier so disappointing, and there's always just enough difference between each one to keep them fresh. The heavily trailered fight between Hulk and Iron Man – in his Hulk-Buster armour, the toy of which I should hope will be filling a lot of people's Christmas stockings this year, mine included – is an undoubted highlight, and the final confrontation is given a real edge by it's inclusion of a get-the-civilians-to-safety aspect. Indeed, it's rare to see a superhero film that takes such care to remind you of the human cost of all this destruction, and it's something that one imagines will be used as a key narrative point in the upcoming Captain America: Civil War.

There are problems. Some of the science is plot-hole filling gobbledegook even by superhero film standards, and the James Spader voiced Ultron, despite the clear relish he brings to his personification of the murderous mechanoid and a few surprising lines, never quite manages to convince as much more than a villain-of-the-week stock type. Indeed, there is a sketchiness to a few of the new characters. Elizabeth Olsen's Scarlett Witch and Aaron Taylor-Johnson's Quicksilver both suffer from underwriting (and ropey accents) and Paul Bettany's Vision is hampered by his late appearance and slight pointlessness (although he does get one of the best sight gags in the whole film). He's there for a reason and we're told that it's important, but it's difficult to work out exactly why.

But you can't be disappointed when faced with such inexhaustible exuberance. Whedon has become the chief custodian of the Marvel cinematic universe, and the Avengers films are the ones that have to convince us of that universe's breadth and depth - that it stretches from the gritty street-level drama of Netflix' recent Daredevil, to the Nordic fantasies of Thor, to the piratical space adventures of Guardians Of The Galaxy. Whedon, with Age Of Ultron, manages to do just that. It's the kind of huge, exhausting, slam-bang rollercoaster that dares you not to be entertained. After two hours and twenty minutes in its company 'tired but elated' was not an expression I had any problem pulling at all.

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